1. Field of the Invention
The present invention relates to a steering axle of a vehicle having a hydrostatic front wheel drive system, and more particularly to a kingpin incorporating a hydraulic swivel coupling adapted to provide a static hydraulic connection between a hydraulic motor mounted directly on a steerable wheel and a source of a pressurized hydraulic fluid mounted on a vehicle body.
2. Description of the Prior Art
Hydrostatic vehicle drive systems have been very popular and commonly used for many vehicles of the "off-highway" type, such as industrial and farming machines, or similar vehicles. Drive wheels of such vehicles are directly driven by fluid pressure actuated hydraulic motors, often mounted directly to the drive wheels, both steerable and nonsteerable. Correspondingly, the vehicles are provided with one or more sources of pressurized hydraulic fluid mounted on a vehicle body, usually in the form of hydraulic pump(s). The vehicular hydrostatic drive system is a highly complex assembly of one or more hydraulic pumps and various valves assemblies interconnected by hydraulic fluid lines. A substantial number of vehicles having the hydrostatic transmission system are provided with a front axle (seldom with a rear axle) having both steering and driving capabilities, wherein a hydraulic motor is mounted directly to the front wheels. A series of hydraulic hoses interconnect the wheel mounted hydraulic motors to the vehicle body mounted hydraulic pump. Naturally, in operation, the hoses experience numerous cycles of bending since the position of the steerable wheels and correspondingly the wheel mounted hydraulic motors change repeatedly. It is a common problem in such a system that the flexible hydraulic hoses used to supply fluid to or from the wheel motor, tend to become rigid under the influence of the pressurized hydraulic fluid, interfere with the steering and, eventually, develop a fatigue that over the period of time could lead to a damage to the hoses.